Listeriosis is a rare but serious illness caused by eating food contaminated with Listeria bacteria. Listeriosis usually causes muscle aches and fever. In pregnant women, listeriosis can cause miscarriage, stillbirth, and serious illness or death in newborns, although it rarely makes the mother seriously ill. Listeriosis can be fatal in the elderly as well as those with compromised immune systems and certain chronic medical conditions like cancer. If you suspect you may have listeriosis, you should call your healthcare provider right away.